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Effects of green tea on weight loss and weight maintenance. A meta-analysis

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Abstract

Different outcomes of the effect of green tea on weight loss (WL) and weight maintenance (WM) have been reported in studies with subjects differing in ethnicity and habitual caffeine intake. To elucidate by meta-analysis whether green tea indeed has a function in body weight regulation. English-language studies about WL and WM after green tea supplementation were identified through PubMed and based on the references from retrieved articles. Out of the 49 studies initially identified, a total of 11 articles fitted the inclusion criteria and provided useful information for the meta-analysis. Effect sizes (mean weight change in treatment versus control group) were computed and aggregated based on a random-effects model. The influence of several moderators on the effect sizes was examined. Catechins significantly decreased body weight and significantly maintained body weight after a period of WL (microcirc=-1.31 kg; P<0.001). Inhibition of this effect by high habitual caffeine intake (>300 mg per day) failed to reach significance (microcirc=-0.27 kg for high and microcirc=-1.60 kg for low habitual caffeine intake; P=0.09). Also, the seemingly smaller effect of catechins in Caucasian (microcirc=-0.82 kg) subjects compared with Asians (microcirc=-1.51 kg; P=0.37) did not reach significance. Interaction of ethnicity and caffeine intake was a significant moderator (P=0.04). Catechins or an epigallocatechin gallate (EGCG)-caffeine mixture have a small positive effect on WL and WM. The results suggest that habitual caffeine intake and ethnicity may be moderators, as they may influence the effect of catechins.
REVIEW
The effects of green tea on weight loss and weight
maintenance: a meta-analysis
R Hursel
1
, W Viechtbauer
2
and MS Westerterp-Plantenga
1
1
Department of Human Biology, Nutrition and Toxicology Research Institute Maastricht (NUTRIM) Maastricht University,
Maastricht, The Netherlands and
2
Department of Methodology and Statistics, Maastricht University, Maastricht,
The Netherlands
Introduction. Different outcomes of the effect of green tea on weight loss (WL) and weight maintenance (WM) have been
reported in studies with subjects differing in ethnicity and habitual caffeine intake.
Purpose. To elucidate by meta-analysis whether green tea indeed has a function in body weight regulation.
Methods. English-language studies about WL and WM after green tea supplementation were identified through PubMed and
based on the references from retrieved articles. Out of the 49 studies initially identified, a total of 11 articles fitted the inclusion
criteria and provided useful information for the meta-analysis. Effect sizes (mean weight change in treatment versus control
group) were computed and aggregated based on a random-effects model. The influence of several moderators on the effect
sizes was examined.
Results.Catechins significantly decreased body weight and significantly maintained body weight after a period of WL
(^
m¼1.31 kg; Po0.001). Inhibition of this effect by high habitual caffeine intake (4300 mg per day) failed to reach significance
(^
m¼0.27 kg for high and ^
m¼1.60 kg for low habitual caffeine intake; P¼0.09). Also, the seemingly smaller effect of
catechins in Caucasian (^
m¼0.82 kg) subjects compared with Asians ( ^
m¼–1.51 kg; P¼0.37) did not reach significance.
Interaction of ethnicity and caffeine intake was a significant moderator (P¼0.04).
Conclusions.Catechins or an epigallocatechin gallate (EGCG)–caffeine mixture have a small positive effect on WL and WM. The
results suggest that habitual caffeine intake and ethnicity may be moderators, as they may influence the effect of catechins.
International Journal of Obesity (2009) 33, 956–961; doi:10.1038/ijo.2009.135; published online 14 July 2009
Keywords: green tea; caffeine; weight loss; weight maintenance; ethnicity
Introduction
Green tea is the most widely consumed beverage next to
water in Asian countries. Moreover, people in Asia have been
aware of the beneficial effects of green tea on health for
already hundreds of years.
1
On the other hand, only recently
is green tea gaining interest in the Westernized world, where
mainly black tea is drunken. Green tea is made from the
fresh leaves of Camellia sinensis, which are processed rapidly
by means of steam to prevent fermentation. Black tea is
made from the same plant as green tea but the leaves endure
an extra enzymatic oxidation step during the processing.
1
The polyphenols in green tea such as epigallocatechin gallate
(EGCG), epigallocatechin, and epicatechin gallate, which are
responsible for its beneficial effects (such as the anti-oxidant
potential and anti-mutagenic capacity) are converted into
thearubigins and theaflavins in black tea.
2
Although black
tea still can improve one’s health, the conversion attenuates
the effects reported after intake of green tea.
3–5
Since the 1990s, green tea is also seen as a natural herb
that can enhance energy expenditure and fat oxidation
and thereby induce weight loss (WL).
6,7
The fact that
an EGCG–caffeine mixture stimulates energy expenditure
cannot be completely attributed to its caffeine content
because the thermogenic effect of an EGCG–caffeine mixture
is greater than that of an equivalent amount of caffeine.
8
Twenty-four hour studies showed a significant increase in
energy expenditure and fat oxidation.
8,9
From these short-
term studies, studies over the longer term originated in
which the effect from an EGCG–caffeine mixture on WL was
studied and soon studies concerning the effect on weight
maintenance (WM) followed.
Almost all of the studies conducted with Asian subjects
have shown positive results about the anti-obesity effects of
Received 30 January 2009; revised 18 May 2009; accepted 2 June 2009;
published online 14 July 2009
Correspondence: R Hursel, Department of Human Biology, Maastricht
University, Universiteitssingel 50, P.O. Box 616, Maastricht, 6200 MD,
The Netherlands.
E-mail: rick.hursel@hb.unimaas.nl
International Journal of Obesity (2009) 33, 956 –961
&
2009 Macmillan Publishers Limited All rights reserved 0307-0565/09
$
32.00
www.nature.com/ijo
catechins.
10–17
On the other hand, studies with Caucasian
subjects reported mixed results.
18–20
Moreover, the
amount of regular caffeine intake may also influence the
effectiveness of catechins. In a study from Westerterp-
Plantenga et al.,
20
it was shown that a regular caffeine intake
of 4300 mg per day in Caucasian subjects diminished the
effects of an EGCG–caffeine mixture on WM, in comparison
with subjects that had a regular caffeine intake of o300 mg
per day.
Hence, the aim of this study was to do a systematic review
and meta-analysis of all the available long-term studies that
have examined the effects of EGCG on WL and WM, to
establish whether catechins contribute to the regulation of
body weight. Possible moderators, such as regular caffeine
intake and ethnicity, are included in the meta-analysis, to
investigate whether they have any impact on the effects
of an EGCG–caffeine mixture on body weight.
Methods
Identification of relevant studies
PubMed was searched for English-language studies that
reported the long-term effects from catechins on WL and
WM. The databases were searched up to July 2008 with
the following keywords: green tea, body weight, WL, WM,
catechins, epigallocatechin gallate or EGCG. References from
the retrieved articles were examined to identify possible
additional articles.
Inclusion and exclusion criteria
A study was valid for inclusion in the review if (a) the study’s
participants were randomly assigned to conditions, (b) the
results allowed a direct comparison of the effects of catechins
(either in the form of catechins versus no catechins or high
dosage versus low dosage catechins) on either WL or WM,
(c) subjects were kept blind to the condition assigned, and
(d) the study lasted for at least 12 weeks. An EGCG–caffeine
mixture tea could either be administered as regular tea or
as capsules. An important exclusion criterion was the use
of any tea other than an EGCG–caffeine mixture (such as
oolong tea).
Data abstraction
Various characteristics were extracted from the original
reports using a standardized data extraction form. We recor-
ded the study’s author(s), year of publication, the duration of
the treatment phase (in weeks), whether the study used a WL
or WM design, and the age range, ethnicity, average body
mass index, gender, and average regular caffeine intake
(in mg per day) of the participants in the study. Moreover, for
each condition, we recorded the number of participants and
the dosage of green tea administered (in mg per day).
For each condition, we calculated or extracted the mean
weight change (in kilograms) between the post-treatment
and the baseline assessment. For WL studies, the baseline
corresponds to the point just before the commencement of
the WL phase, whereas for WM studies, the baseline
corresponds to the point before the commencement of the
WM phase. The post-treatment mean was always based on
the time point immediately following the intervention.
Regardless of the study design, negative values for the mean
change, therefore, indicate WL, a value of zero indicates no
change, and positive values indicate an increase in the body
mass on average. The effect size measure for the meta-
analysis was then the difference between the mean change
value for the treatment minus the mean change value for the
control group. Negative values for the observed effect size,
therefore, indicate more WL (or less weight gain) on average
in the treatment compared with the control group and,
therefore, a positive treatment effect of the EGCG–caffeine
mixture on WL/WM.
The following three variables were a priori chosen for
examination as potential moderators: the ethnicity of the
participants (either Asian or Caucasian), the average regular
caffeine intake of the participants in the study (either low
or high, with 300 mg per day being the cutoff), and the
difference in dosage of the EGCG–caffeine mixture adminis-
tered in the treatment and the control group.
Statistical analysis
The effect size estimates were aggregated based on a random-
effects model, using restricted maximum-likelihood (REML)
estimation to estimate the amount of heterogeneity in the
effect sizes.
21
We report the estimated average effect (^
m), the
estimated amount of heterogeneity in the true effects (^
t2),
and the estimated percentage of the total amount of
variability that can be attributed to heterogeneity (I
2
).
Corresponding 95% confidence intervals are given for all of
these statistics. We also provide the results from the test for
heterogeneity. The moderators were examined individually
and in combination using mixed-effects models, again using
REML estimation for the amount of (residual) heterogeneity.
For these models, we report the estimated effect sizes within
each level of a moderator with corresponding 95%
confidence intervals.
Results
Forty-four potentially relevant studies were found initially.
From these, 15 review articles were excluded immediately, as
these contributed no additional data besides the original
studies, which were already included. Another 13 studies
were excluded on the basis of title and abstract, as these
were studies conducted with animals. Five articles from
Asian authors were obtained through personal communi-
cation.
10–12,14,17
Four of them only had an English abstract
Effects of green tea on body composition
R Hursel et al
957
International Journal of Obesity
and were further written in Japanese. These articles were sent
to us with an English translation, as we contacted the
institution (Kao Corporation, Tokyo, Japan) where Nagao
et al.
13
are employed, after finding their study in PubMed.
Information from the fifth Asian study by Wang et al.
17
was
also obtained through personal communication, as the
results were not published during the data abstraction. Of
the remaining 21 studies, 9 did not use green tea (e.g.,
oolong tea) or did not provide sufficient information to
compute effect sizes. Only one study was excluded because
of the time period, as it lasted for 8 weeks. No studies
were excluded because of lack of randomization or blinding.
Finally, 11 articles fulfilled the inclusion criteria.
10–20
Figure 1
shows the process of study selection.
The selected articles all had comparable designs: in the WL
studies,
10–18
participants immediately started to consume an
EGCG–caffeine mixture for 12 weeks following randomiza-
tion; in the WM studies,
19,20
subjects first lost weight for
4 weeks using a very low energy diet, followed by randomi-
zation and then an EGCG–caffeine mixture supplementation
for either 12 or 13 weeks (Table 1). In all but one study,
17
subjects were randomly assigned to two conditions, with
seven studies
10,15–20
using a true placebo group and the
remaining four studies
11–14
comparing a high with a low
dose of an EGCG–caffeine mixture.
Almost every article reported the relevant information
about the moderators, for instance as an important inclusion
criterion. If regular caffeine intake was not reported by the
Asian studies, it was assumed to be low.
22
From three studies it was possible to calculate more than
one effect size estimate. Kozuma et al.
10
reported their results
separately for men and women, which, therefore, yields two
effect size estimates for the meta-analysis. Also, the data
from Westerterp-Plantenga et al.
20
allowed the calculation of
two estimates, one for subjects with high and the other for
subjects with low regular caffeine intake. Finally, three effect
size estimates were obtained from the study by Wang et al.,
17
as it contained three treatment groups that received either a
different dosage or an equivalent dosage distributed in a
different number of servings. A total of 15 effect size
estimates could, therefore, be extracted from the 11 studies.
Figure 2 shows a plot of the individual effect size estimates
with corresponding 95% confidence intervals.
The random-effects model indicated a modest, but sig-
nificant positive effect of catechins on WL/WM (^
m¼1.31,
95% CI: 2.05 to 0.57; Po0.001). Therefore, it is estimated
that subjects in the treatment groups lost on average
1.31 kg more weight (or gained on average 1.31 kg less
weight) than people in the control groups. Removal of any
individual study from the meta-analysis did not alter this
conclusion (with ^
mvalues ranging from 1.07 to 1.47; all
Po0.004). However, the results were clearly hetero-
geneous (^
m¼1.13 with 95% CI: 0.25 to 3.80; I
2
¼94% with
95% CI: 77% to 98.0%; test for heterogeneity: Po0.001).
The difference in dosage of the EGCG–caffeine mixture
between the treatment and the placebo group was not a
significant moderator, whether examined in combination
with the other two moderators or individually (P¼0.34 and
0.76, respectively). Although the average effect was larger for
studies with Asian (^
m¼1.51, 95% CI: 2.37 to 0.65) than
Caucasian (^
m¼0.82, 95% CI: 2.13 to 0.50) samples, the
difference did not reach statistical significance (P¼0.19
when examined in combination with the other two
moderators and P¼0.37 when examined individually).
The estimated effect was larger for samples with a low
(^
m¼1.60, 95% CI: 2.38 to 0.83) in comparison to a
moderate-to-high regular caffeine intake (^
m¼0.27, 95% CI:
1.63 to 1.10). The difference was significant when
examined in combination with the other moderator, but
not when examined individually (P¼0.04 and P¼0.09,
respectively). The estimated amount of (residual) hetero-
geneity was equal to ^
t2¼0.92 after inclusion of this
moderator in the model, suggesting that B19% of the total
amount of heterogeneity could be accounted for based on
information about the regular caffeine intake of the samples
in the set of studies.
Discussion
The results of this meta-analysis show that an EGCG–
caffeine mixture has an effect on WL and on WM after a
period of negative energy balance. It is also shown that
interaction of ethnicity and habitual caffeine intake is a
44 articles were found in
PubMed (N=44)
49 studies were included
(N=49)
11 articles were included
5 Articles obtained via
personal communication
(N=5)
23 articles excluded
Review studies (N=15)
Not sufficient
information (N=5)
Not green tea (N=4)
Duration of study too
short (N=1)
36 studies were included
(N=36)
13 articles excluded on
basis of title or abstract
(N=13)
Figure 1 Process of study selection.
Effects of green tea on body composition
R Hursel et al
958
International Journal of Obesity
moderator. Dosage of catechins in the treatment or in the
placebo did not have any significant effect on the outcome
of the studies that were included.
However, the overall result implies some heterogeneity.
This may be caused by studies differing in the possible
moderators ethnicity and habitual caffeine intake. In
particular, all Asian studies had a low caffeine intake and
nearly all Caucasian studies had a high caffeine intake. Only
one treatment group of the Westerterp-Plantenga et al.
20
study had a low caffeine intake. Although caffeine intake was
a significant moderator when examined together in a model
including ethnicity, inclusion of more studies with both
ethnicities with different amounts of caffeine intake would
provide a clearer picture of how these moderators influence
the effectiveness of catechins.
Interaction between the possible moderators maybe due to
differences in allele frequencies of polymorphisms between
ethnicities. For instance, people who drink caffeine regularly
not only get habituated to the effects of caffeine, but also
tolerate caffeine intake. Cornelis et al.
23
showed that
Hispanic Americans with an ADORA2A 1083TT genotype
are more likely to limit their caffeine intake than the CC and
CT genotype. These persons appeared to be more sensitive
for the differences between caffeine and the adenosinergic
system. This genotype codes for the A
2a
receptor, at which
caffeine antagonizes the actions of adenosine, a key process
in the stimulating properties of caffeine. CYP1A2, which
codes for the enzymes of cytochrome P450 (the metabolizers
of caffeine), does not seem to have a function.
23
Therefore, it
may well be that the habitually low caffeine consumers do
not tolerate high amounts of caffeine intake and, therefore,
react more sensitively to the small amount of caffeine added
to the green tea mixture. When the allele frequencies of the
genes coding for the activity of the enzyme differ between
ethnic groups, this may explain the observed differences in
response to the treatment. For this reason, ethnicity was
included as a moderator. Although ethnicity was not a
significant moderator, the results suggest that it may affect
the effect an EGCG–caffeine mixture has on thermogenesis
as the Asian subjects lost more weight than the Caucasian
subjects. However, before the moderating role of ethnicity
can be examined in more detail, additional studies with
Caucasian samples should be conducted to offset the larger
number of studies with Asian samples.
The inhibition of several enzymes may be the mechanism
by which the components of green tea induce WL/WM.
Catechins inhibit the catechol O-methyltransferase (COMT)
and caffeine inhibits phosphodiesterase. Levels of norepine-
phrine and cAMP rise because degradation by these enzymes
is ceased. Consequently, parasymphatic activity is in-
creased.
8
This phenomenon does not appear equally clear
in all ethnic groups because of the differences in relevant
enzyme activity, causing differences in sensitivity for these
ingredients. In that respect, Hodgson et al.
24
stated that there
is a wide variability in flavonoid O-methylation, a major
pathway of flavonoid metabolism, by the enzyme COMT.
Table 1 Characteristics of all included articles
Author Year Duration
(weeks)
Sample
Size (n)
BMI
(kg/m
2
)
Gender Age
(years)
Dosage
(mg per day)
Regular caffeine
intake (mg per day)
Ethnicity Outcome
Kovacs et al.
19
2004 13 GT ¼51 PL ¼53 25–35 M/F 18–60 GT ¼573 PL ¼04300 Caucasian No weight maintenance
Westerterp-Plantenga et al.
20
2005 13 GT ¼19 PL ¼19 25–35 M/F 18–60 GT ¼270 PL ¼0o300 Caucasian Weight maintenance
Westerterp-Plantenga et al.
20
2005 13 GT ¼19 PL ¼19 25–35 M/F 18–60 GT ¼270 PL ¼04300 Caucasian No weight maintenance
Diepvens et al.
18
2005 13 GT ¼23 PL ¼23 25–31 F 19–57 GT ¼1207 PL ¼04300 Caucasian No weight loss
Hase et al.
14
2001 12 GT ¼12 PL ¼11 18.5–30 M 27–47 GT ¼483 PL ¼119 o300 Japanese Weight loss
Nagao et al.
12
2001 12 GT ¼13 PL ¼12 24.3–34.6 M 24–49 GT ¼541 PL ¼130 o300 Japanese Weight loss
Tsuchida et al.
11
2002 12 GT ¼39 PL ¼41 24–30 M/F 30–65 GT ¼588 PL ¼126 o300 Japanese Weight loss
Kozuma et al.
10
2005 12 GT ¼53 PL ¼64 25–35 F 20–65 GT ¼540 PL ¼0o300 Japanese Weight loss
Kozuma et al.
10
2005 12 GT ¼54 PL ¼55 25–35 M 20–65 GT ¼540 PL ¼0o300 Japanese Weight loss
Nagao et al.
13
2007 12 GT ¼123 PL ¼117 24–30 M/F 25–55 GT ¼583 PL ¼96 o300 Japanese Weight loss
Auvichayapat et al.
15
2008 12 GT ¼30 PL ¼30 425 M/F 40–60 GT ¼750 PL ¼0o300 Thai Weight loss
Hsu et al.
16
2008 12 GT ¼41 PL ¼37 427 F 16–60 GT ¼491 PL ¼0o300 Taiwanese No weight loss
Wang et al.
17
2008 12 GT ¼49 PL ¼43 X24 o35 M/F 18–50 GT ¼440 PL ¼0o300 Chinese No weight loss
Wang et al.
17
2008 12 GT ¼47 PL ¼43 X24 o35 M/F 18–50 GT ¼468 PL ¼0o300 Chinese No weight loss
Wang et al.
17
2008 12 GT ¼43 PL ¼43 X24 o35 M/F 18–50 GT ¼880 PL ¼0o300 Chinese Weight loss
Abbreviations: BMI, body mass index; F, female; GT, EGCG–caffeine mixture group; M, male; PL, placebo group.
Effects of green tea on body composition
R Hursel et al
959
International Journal of Obesity
The inter-individual variability of the activity of COMT
could vary as much as three-fold.
24
Moreover, COMT enzyme
activity differs between ethnic groups,
25
in that Asian
populations have a higher frequency of the thermostable,
high activity enzyme, COMT
H
allele (Val/Val polymorphism)
than the Caucasian populations. The Caucasian populations
have a higher frequency of the thermolabile, low activity
enzyme, COMT
L
allele (Met/Met polymorphism).
3
In all, 50%
of Caucasians are homozygous for the COMT
L
allele (25%)
and COMT
H
allele (25%). The other 50% is heterozygous
(Val/Met polymorphism).
25
This may explain the difference
in sensitivity to interventions with EGCG–caffeine mixtures,
and why, in some studies with Caucasian subjects, no effect
was seen after ingestion of an EGCG–caffeine mixture. The
observations described above suggest interaction between
the two possible moderators. Not until the two moderators
were taken together, the difference in estimated effect
between samples with low and moderate-to-high regular
caffeine intake became significant, probably because of
coincidence of polymorphisms ADORA2A, COMT, and
ethnicity.
The results of the meta-analysis also show that the
difference in dosage of the catechins in the EGCG–caffeine
mixture between treatment and control groups had no effect
on the size of the effect. This finding is consistent with the
results from the study of Berube-Parent et al.
9
in which four
different mixtures of EGCG and caffeine with a different
dosage of catechins were examined. The results from that
study showed that all mixtures increased 24-h energy
expenditure and that the increase was similar for all doses
of EGCG in the mixtures, which was also found in the study
from Wang et al.
17
Taken together, this meta-analysis has shown that EGCG–
caffeine mixtures have a positive effect on WL and on WM.
-8 -6 -4 -2 0 2 4
Effect Size (in kg)
Kovacs, 2004
Diepvens, 2005
Westerterp-Plantenga, 2005
Westerterp-Plantenga, 2005
Nagao, 2007
Hase, 2001
Nagao, 2001
Auvichayapat, 2008
Tsuchida, 2002
Kozuma, 2005
Kozuma, 2005
Hsu, 2008
Wang, 2008
Wang, 2008
Wang, 2008
Caucasian, caffeine = 1
Caucasian, caffeine = 1
Caucasian, caffeine = 1
Caucasian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Asian, caffeine = 0
Overall Effect from
Random-Effects Model
Figure 2 Forest plot of the individual effect size estimates (mean weight change within the treatment group minus mean weight change within the control group)
with corresponding 95% confidence intervals (caffeine ¼0/1 for low (0) or moderate-to-high (1) regular caffeine intake).
Effects of green tea on body composition
R Hursel et al
960
International Journal of Obesity
Moreover, it also shows that habitual caffeine intake and
ethnicity may be moderators, especially because of inter-
actions of the different ADORA2A and COMT polymor-
phisms and ethnicity, whereas different doses of catechins
do not have a significantly different effect. Experimental
research is needed to find out whether and to what
extent people are genetically predisposed for the effect of
EGCG–caffeine mixtures.
Conflict of interest
The authors declare no conflict of interest.
Acknowledgements
RH and MSW-P designed the study. RH collected and
prepared the data. WV analyzed the data. RH and WV wrote
the manuscript and MSW-P contributed to the interpretation
of the data and reviewed the manuscript. The study was
executed under the supervision of MSW-P.
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Effects of green tea on body composition
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... Pese a que se han publicado varias revisiones de la literatura científi ca sobre el papel potencial que puede tener el té verde como coadyuvante en la pérdida de peso y en la prevención del weight cycling (conocido como "efecto yoyó") [18][19][20] , su revisión de forma sistemática y crítica es menos abundante [21][22][23] . Aunque se dispone de revisiones sistemáticas y metaanálisis [21][22][23] , existen importantes consideraciones de inclusión y exclusión de estudios (consumo basal de cafeína y catequinas y cuantifi cación del consumo de ambas sustancias, control de su ingesta en los grupos control, alteraciones y enfermedades que pueden afectar espontáneamente al peso de los individuos sujetos a estudio, duración de la intervención o control de otros aspectos terapéuticos, como la dieta y el ejercicio físico) así como de análisis de subgrupos (individuos caucásicos y individuos asiáticos) que, según la opinión de los autores de esta revisión, podrían ejercer como factores de confusión. ...
... Pese a que se han publicado varias revisiones de la literatura científi ca sobre el papel potencial que puede tener el té verde como coadyuvante en la pérdida de peso y en la prevención del weight cycling (conocido como "efecto yoyó") [18][19][20] , su revisión de forma sistemática y crítica es menos abundante [21][22][23] . Aunque se dispone de revisiones sistemáticas y metaanálisis [21][22][23] , existen importantes consideraciones de inclusión y exclusión de estudios (consumo basal de cafeína y catequinas y cuantifi cación del consumo de ambas sustancias, control de su ingesta en los grupos control, alteraciones y enfermedades que pueden afectar espontáneamente al peso de los individuos sujetos a estudio, duración de la intervención o control de otros aspectos terapéuticos, como la dieta y el ejercicio físico) así como de análisis de subgrupos (individuos caucásicos y individuos asiáticos) que, según la opinión de los autores de esta revisión, podrían ejercer como factores de confusión. Asimismo, los autores de sendas revisiones 21,22 (excepto Jurgens TM et al. 2012 23 ) no establecen una clara diferencia entre los resultados estadísticamente significativos y los resultados clínicamente relevantes. ...
... Asimismo, se buscaron más estudios potencialmente relevantes mediante el sistema que el manual Cochrane defi ne como pearling (o "encontrar perlas") revisando los estudios incluidos en los dos metaanálisis publicados hasta la fecha 21,22 . No se analizó el metaanálisis publicado por Jurgens TM et al. 2012 23 , ya que en el momento de la obtención de dicha publicación, el presente metaanálisis ya estaba en fase de análisis de los datos. ...
... In recent years, research has focused on effects of exercise training, alone or in combination with GT ingestion, related to fat metabolism [17][18][19][20], body composition [17,[20][21][22] and cardiovascular risk factors such as blood lipids profile [17,20,21] and blood pressure [11]. Since exercise training may be efficient only in the longer term, it has hypothesized that GT supplementation would boost the effect of exercise training on theses parameters through its specific thermogenic effects [20,23], antioxidative properties [24] and/or other potential therapeutic health benefits. In this context, Rostamian and Bijeh [17] reported that short-term aerobic training (i.e., 2 weeks) along with GT consumption was more effective in reducing serum triglycerides (TG) and visceral fat levels in sedentary postmenopausal women. ...
... To date, several mechanisms have been proposed regarding the effects of GT intake on human health. GT constituents, especially catechins, may induce specific thermogenic effects due to the inhibition of catechol-o-methyl transferase (COMT) with the subsequent increased activity of catecholamine, cyclic adenosine monophosphate (cAMP) and lipolysis [23]. As a result, these effects may lead to enhance whole-body FO [28,67], and GT ingredients may be associated with a variety of health-related metabolic effects including reduced adipose tissue [53], improved BMI [67], and lowered LDL [51]. ...
Article
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Background Green tea (GT) consumption may influence fat oxidation (FO), body composition and blood lipid profile in human subjects. Therefore, this study aimed to review the current literature regarding the interactive effect of aerobic and resistance training with GT ingestion on these parameters. Methods Electronic searches were performed in Google Scholar, PubMed, Elsevier, Science Direct, and national databases. Only studies on human subjects that included GT intervention and aerobic or resistance exercise from any date to May 30, 2021 were reviewed. Results Twenty-seven papers (n = 831 participants) were included. From these, 12 studies addressed the acute or short-term effect of GT consumption on substrate oxidation during exercise, 2 studies assessed the long-term effect of GT consumption and aerobic exercise on substrate oxidation during exercise, 9 studies examined the short-term or long-term effects of GT intake and aerobic exercise on substrate oxidation or cardiometabolic risk factors, and 4 studies investigated the long-term effects of GT consumption and resistance training on substrate oxidation or cardiometabolic risk factors. Conclusions Short-term consumption of GT may have positive metabolic effects during moderate-intensity exercise in inactive people or those who exercise recreationally. Likewise, a combination of moderate-intensity aerobic training and GT consumption for a minimum period of 8 to 10 weeks can increase FO during exercise in healthy individuals. Regular resistance training combined with GT consumption may have potential benefits in enhancing body composition, lowering triglyceride, and increasing high-density lipoprotein in sedentary obese/overweight people.
... Findings from human trials support that either long-term or short-term consumption of tea polyphenols can improve metabolic health and body weight of obese subjects besides several other effects (Table 2) (Brown et al. 2009;Chen et al. 2016). Yet, a meta-analysis aimed at weight loss and weight maintenance pointed out a significant heterogeneity in the effect sizes of long-term supplementation of catechins (Hursel, Viechtbauer, and Westerterp-Plantenga 2009). A randomized double-blind trial was not able to conclude that the intake of EGCG-enriched green tea extract lowered the levels of total cholesterol and low-density lipoprotein-cholesterol with the standard deviations of data reaching 86.8% (211.4 ± 9.9 mg/dL) and 49.0% (214.7 ± 7.2 mg/dL), respectively (Basu et al. 2010). ...
... A meta-analysis pointed out that Asian subjects benefited more from tea polyphenols than Caucasian subjects (Hursel, Viechtbauer, and Westerterp-Plantenga 2009). This indicates that ethnicity may also influence the anti-obesity effects of catechins. ...
Article
Tea polyphenols have been extensively studied for their preventive properties against cardiometabolic diseases. Nevertheless, the evidence of these effects from human intervention studies is not always consistent, mainly because of a large interindividual variability. The bioavailability of tea polyphenols is low, and metabolism of tea polyphenols highly depends on individual gut microbiota. The accompanying reciprocal relationship between tea polyphenols and gut microbiota may result in alterations in the cardiometabolic effects, however, the underlying mechanism of which is little explored. This review summarizes tea polyphenols-microbiota interaction and its contribution to interindividual variability in cardiometabolic effects. Currently, only a few bacteria that can biodegrade tea polyphenols have been identified and generated metabolites and their bioactivities in metabolic pathways are not fully elucidated. A deeper understanding of the role of complex interaction necessitates fully individualized data, the integration of multiple-omics platforms and development of polyphenol-centered databases. Knowledge of this microbial contribution will enable the functional stratification of individuals in the gut microbiota profile (metabotypes) to clarify interindividual variability in the health effects of tea polyphenols. This could be used to predict individual responses to tea polyphenols consumption, hence bringing us closer to personalized nutrition with optimal dose and additional supplementation of specific microorganisms.
... In addition to a cold environment and exercise training, thermogenesis in BAT can also be induced by dietary interventions in both rodents (Table 1) and humans ( Table 2). Catechins have been shown to reduce body fat mass by 2-3% in humans when ingested regularly [151][152][153][154]. Moreover, several studies describe specific dietary components such as menthol [155][156][157][158] or capsaicin, found in spicy foods [159,160], whose consumption leads to an activation of UCP1-dependent thermogenesis in human BAT and to the prevention of high-fat diet-induced obesity. ...
Article
The discovery of functional brown adipose tissue (BAT) in adult humans and the possibility to recruit beige cells with high thermogenic potential within white adipose tissue (WAT) depots opened the field for new strategies to combat obesity and its associated comorbidities. Exercise training as well as cold exposure and dietary components are associated with the enhanced accumulation of metabolically-active beige adipocytes and BAT activation. Both activated beige and brown adipocytes increase their metabolic rate by utilizing lipids to generate heat via non-shivering thermogenesis, which is dependent on uncoupling protein 1 (UCP1) in the inner mitochondrial membrane. Non-shivering thermogenesis elevates energy expenditure and promotes a negative energy balance, which may ameliorate metabolic complications of obesity and Type 2 Diabetes Mellitus (T2DM) such as insulin resistance (IR) in skeletal muscle and adipose tissue. Despite the recent advances in pharmacological approaches to reduce obesity and IR by inducing non-shivering thermogenesis in BAT and WAT, the administered pharmacological compounds are often associated with unwanted side effects. Therefore, lifestyle interventions such as exercise, cold exposure, and/or specified dietary regimens present promising anchor points for future disease prevention and treatment of obesity and T2DM. The exact mechanisms where exercise, cold exposure, dietary interventions, and pharmacological treatments converge or rather diverge in their specific impact on BAT activation or WAT browning are difficult to determine. In the past, many reviews have demonstrated the mechanistic principles of exercise- and/or cold-induced BAT activation and WAT browning. In this review, we aim to summarize not only the current state of knowledge on the various mechanistic principles of diverse external stimuli on BAT activation and WAT browning, but also present their translational potential in future clinical applications.
... Then, ultimately, microbiota may concur to improve the health effects of EGCG. In addition to cancer cell cytotoxicity, indirect advantages of EGCG on cancer onset and development are also related to the metabolic (antidiabetic and contrasting obesity effects) (Hursel et al., 2009;Hara-Terawaki et al., 2017;Quezada-Fernández et al., 2019), antioxidative, and anti-inflammatory actions of EGCG (Chen et al., 2018), all these conditions being clearly associated with cancer development (Thielecke and Boschmann, 2009;Yang et al., 2016;Oz, 2017;Potenza et al., 2020). ...
Article
Full-text available
Chemoprevention is a strategy aimed to not only reduce the risk but also delay the development or recurrence of cancer. An ideal chemopreventive agent is not dangerous and ought not to result in side effects or damage to human health. In this context, epigallocatechin-3-gallate (EGCG) is considered a suitable chemopreventive agent, but its clinical use is limited by many factors, namely, the difference in source, administration, individual metabolism, absorption, and distribution. Genetic and dietary differences greatly cause this variability, which has limited the rational use of EGCG in chemoprevention and, particularly, the definition of a safe and efficient concentration. In the present mini review, the main limitations to a complete understanding of the use of EGCG as a chemopreventive agent will be briefly illustrated. This review also indicates the introduction and trialing of lipid-based nanoparticles (NPs) as a proper strategy to deliver EGCG at a well-defined concentration for better investigation of the chemopreventive activity. Finally, some examples of cancers that might benefit from EGCG treatment in different stages of the disease are proposed.
... The effects of green tea found in the literature on body weight, in different populations, corroborate our findings. Besides reducing body weight, green tea is also associated with a protective effect on weight gain, even with increased energy intake after a period of interruption of supplementation [24] , weight maintenance [25] , and probability to maintain weight loss greater than or equal to 5% [26] , when compared with studies with a placebo group. ...
Article
Among the main consequences of PCOS, are mentioned menstrual dysfunction, infertility, hyperandrogenism, insulin resistance, weight gain and, in aggravated cases, it can become a risk factor for the development of metabolic syndromes and cardiovascular diseases. We hypothesize that green tea can be an option to complement the treatment of PCOS. Thus, this systematic review aims to evaluate the effects of green tea supplementation in women with PCOS. We searched for randomized controlled trials (RCTs) that evaluated women with PCOS who received green tea compared to placebo in the electronic databases: MEDLINE via PubMed, EMBASE via Elsevier, Cochrane Library, LILACS via BVS and Web of Science, using the terms: “polycystic ovary syndrome”, “green tea”, “Camellia sinenses”, “epigallocatechin gallate”. The outcomes listed in the study protocol were: body weight, fasting insulin, body mass index, body fat percentage, daily caloric intake, waist circumference, hip circumference, waist/hip ratio. Four double-blind RCT were included, with a total of 169 women: 85 in the green tea group (GTG) and 84 in the placebo group (PG). We found a significant lower body weight (kg) for green tea group (MD -2.80; 95%CI -5.25 to -0.35; P = 0.03; I² = 0%, four studies, 169 participants, very low-quality evidence). Green tea has potential positive effects for the reduction of weight and future studies will probably confirm the estimated effect size, thus we reasonably expect as an option of adjuvant treatment in the clinical management of PCOS. Registration number: CRD42021226296.
... Moreover, we noticed that supplementation with green tea has a positive effect on the hematological parameters in lead-intoxicated animals. Previous studies also reported the hematological changes induced by lead intoxication in albino mice [1,25]. It was found that RBCs have a high affinity for lead and approximately 99% of the lead present in the blood is bound to erythrocytes, which makes them more vulnerable to oxidative damage than many other cells [26]. ...
Article
Full-text available
The use of natural products as therapeutic agents is rapidly growing recently. In the current study, we investigated the protective effects of green tea supplementation on lead-induced toxicity in mice. Forty albino mice were divided into four groups as follows: A: control group; B: green tea receiving group; C: lead-intoxicated group; and D: lead-intoxicated group supplemented with green tea. At the end of the experiment, the animals were tested for neurobehavioral and biochemical alterations. Green tea was analyzed through Gas Chromatography–Mass Spectrometry (GC/MS) analysis. We found that supplementation with green tea ameliorated the lead-associated increase in body weight and blood glucose. Green tea supplementation also changed the blood picture that was affected due to lead toxicity and ameliorated lead-induced dyslipidemia. The group of mice that were supplemented with green tea has shown positive alterations in locomotory, anxiety, memory, and learning behaviors. The GC/MS analysis revealed many active ingredients among which the two most abundant were caffeine and 1,2-benzenedicarboxylic acid, mono(2-ethylhexyl) ester. We concluded that green tea supplementation has several positive effects on the lead-induced neurotoxicity in mice and that these effects may be attributed to its main two active ingredients.
... The outcomes obtained from the meta-analysis demonstrated that an EGCC-caffeine mixture affects WL and WM long after the negative balance of energy. Moreover, the interchange of ethnicity and habitual caffeine intake was shown a facilitator(Pawar, 2015;Hursel, 2009).Regarding the use of lemons in our study, it was concluded that 29.5% reduced weight in study participants and this was a similar finding with Negar et al., (2016), who found that group 1 had a substantial reduction in overall cholesterol (P =0.001), lowdensity lipoprotein-cholesterol (P =0.001), and fibrinogen (P =0.001), as compared to the other classes. Group 1, with respect to groups 3 and 4 (37 ± 10, P = 0.01) (24 ± 1, P = 0.02), a larger decrease in the systolic and diastolic blood pressure was observed respectively; Additionally, the combined group has a significant decrease in body mass index as compared to the lemon juice and control groups (P = 0.04). ...
Article
Full-text available
Background: Obesity is a common and morbid disease. There are different methods to reduce weight. The most common surgical methods to reduce weight are bariatric surgical procedures which include gastric bypass, adjustable gastric banding and sleeve gastrectomy. Many drugs have been developed for the long-term management of obesity to cause a positive energy balance. Some herbal medicine products are taken as liquids or tea prior to eating, such as chamomile, green tea can assist in reducing weight. Others spices such as ginger help in weight loss. Many researches suggest that exercise is more effective in the prevention of overweight and obesity than its reversal. The aim of this study is to compare the use of surgery, drugs, exercise, and focusing on herbal remedies regarding weight reduction and to help in raising awareness among people to maintain healthy lifestyle. Method: A Cross-sectional study has been done among people in Ha'il, KSA. The data are collected by distributing online questionnaire. Statistical analysis has been done with (SPSS) V 23.0 (Chi-Square Tests considering level of significance P≤ 0.001 and P≤ 0.05). Result: The result of this study showed that a total 552 of participants in Hail, 29 (6.4%) female and 2 (2.2%) male had used herbs to reduce their weight and the most common used herbs were green tea, lemon, ginger and cinnamon respectively. 21 participants (4.6%) of female and 5 (5.6%) of male prefer surgery for weight loss. The 166 (36.4%) of female, while the male 36 (40.4%) make use of exercise to reduce the weight. Also, 3 (0.7%) of female used the drug, while male never used. Conclusion: The study concluded that the most common method used was exercise. The others were herbs, surgery and drugs, respectively.
... Moreover, from the available meta-analyses, it was also reported that catechins have the propensity of reducing BMI, BW and WC, increasing metabolic rate even at low dose (ca. 300 mg per day) (267)(268)(269). However, current clinical data, recently meta-analyzed by Haghighatdoost and Hariri, do not suggest benefits of catechins on inflammatory mediators, such as CRP, TNF-α, and IL-6 (270). ...
Article
Full-text available
The human diet and dietary patterns are closely linked to the health status. High-calorie Western-style diets have increasingly come under scrutiny as their caloric load and composition contribute to the development of non-communicable diseases, such as diabetes, cancer, obesity, and cardiovascular disorders. On the other hand, calorie-reduced and health-promoting diets have shown promising results in maintaining health and reducing disease burden throughout aging. More recently, pharmacological Caloric Restriction Mimetics (CRMs) have gained interest of the public and scientific community as promising candidates that mimic some of the myriad of effects induced by caloric restriction. Importantly, many of the CRM candidates activate autophagy, prolong life- and healthspan in model organisms and ameliorate diverse disease symptoms without the need to cut calories. Among others, glycolytic inhibitors (e.g., D-allulose, D-glucosamine), hydroxycitric acid, NAD+ precursors, polyamines (e.g., spermidine), polyphenols (e.g., resveratrol, dimethoxychalcones, curcumin, EGCG, quercetin) and salicylic acid qualify as CRM candidates, which are naturally available via foods and beverages. However, it is yet unclear how these bioactive substances contribute to the benefits of healthy diets. In this review, we thus discuss dietary sources, availability and intake levels of dietary CRMs. Finally, since translational research on CRMs has entered the clinical stage, we provide a summary of their effects in clinical trials.
Article
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The meta-analytic random effects model assumes that the variability in effect size estimates drawn from a set of studies can be decomposed into two parts: heterogeneity due to random population effects and sampling variance. In this context, the usual goal is to estimate the central tendency and the amount of heterogeneity in the population effect sizes. The amount of heterogeneity in a set of effect sizes has implications regarding the interpretation of the meta-analytic findings and often serves as an indicator for the presence of potential moderator variables. Five population heterogeneity estimators were compared in this article analytically and via Monte Carlo simulations with respect to their bias and efficiency.
Article
The body fat reducing effect of tea catechins was previously confirmed in humans. The effects of tea catechins for reducing body fat were thus studied as basis for actual application. Three experiments on healthy male adults (n=82) were conducted to determine the effects of long-term tea catechins administration on body fat and biochemical blood parameters. First experiment: tea catechins were given as oolong tea-like beverage for 12 weeks. In 600 and 900 mg groups, visceral fat was significantly loss than in the control (600 mg group p=0.0317, 900 mg group p=0.0098). The effects were more pronounced at greater of tea catechins administration. No significant changes in biochemical blood parameters including fat-soluble vitamins were detected. Second experiment : oolong tea-like beverage containing tea catechins at nearly same amounts on in the 600 mg group was given for 20 weeks. Abdominal fat, including visceral fat, was significantly loss than in the control (total fat area p<0.0001, visceral fat area p=0.0004, subcutaneous fat area p=0.0001). Plasma PAI-1 was also significantly decreased (p=0.0080). Third experiment : green tea-like (GT group) and oolong tea-like (OT group) beverages containing approximately 540 mg tea catechins were given for 12 weeks. In the two groups, visceral fat was significantly loss than in the control (GT group p=0.0284, OT group p=0.0095) and the effects of two beverages were similar. Long-term tea catechins administration at 500 to 600 mg/day in humans would thus appear to reduce body fat without influencing fat-soluble vitamins, of which the absorption may be inhibited, and various serum and plasma indices regardless of the kind of beverages.
Article
We assessed the effect of ingestion of green tea (GT) extract along with a low-energy diet (LED) on resting energy expenditure (REE), substrate oxidation and body weight as GT has been shown to increase energy expenditure and fat oxidation in the short term in both animals and people. Forty-six overweight women (BMI 27 center dot 6 (sd 1 center dot 8) kg/m(2)) were fed in energy balance from day 1 to day 3, followed by a LED with GT (1125 mg tea catechins +225 mg caffeine/d) or placebo (PLAC) from day 4 to day 87. Caffeine intake was standardised to 300 mg/d. Energy expenditure was measured on days 4 and 32. Reductions in weight (4 center dot 19 (sd 2 center dot 0) kg PLAC, 4 center dot 21 (sd 2 center dot 7) kg GT), BMI, waist:hip ratio, fat mass and fat-free mass were not statistically different between treatments. REE as a function of fat-free mass and fat mass was significantly reduced over 32 d in the PLAC group (P < 0 center dot 05) but not in the GT group. Dietary restraint increased over time (P < 0 center dot 001) in both groups, whereas disinhibition and general hunger decreased (P < 0 center dot 05). The GT group became more hungry over time and less thirsty, and showed increased prospective food consumption compared with PLAC (P < 0 center dot 05). Taken together, the ingestion of GT along with a LED had no additional benefit for any measures of body weight or body composition. Although the decrease in REE as a function of fat-free mass and fat mass was not significant with GT treatment, whereas it was with PLAC treatment, no significant effect of treatment over time was seen, suggesting that a robust limitation of REE reduction during a LED was not achieved by GT.
Article
To examine the anti-obesity effects of tea catechins in humans, a trial study using healthy male subjects (27-47 years). Comprising in equal number a low dose catechin (LDC) group (n=11) and high dose catechin (HDC) group (n=12). The groups were administered catechins at 118.5 mg and 483.0 mg a day for 12 weeks, respectively. At 4 and 12 weeks, effect evaluation was made based on change in weight, body mass index (BMI), waist circumference, body fat ratio and abdominal fat as determined by computed tomography (CT) and triacylglycerol, total cholesterol, free fatty acid, glucose, insulin and total plasminogen activator inhibitor-1 (PAI-1) in serum. In the HDC group, at 12 weeks, weight, BMI, waist circumference, body fat ratio, abdominal fat and total cholesterol, glucose, insulin, PAI-1 in serum were noted to have significantly decreased from values at 0 week. In the LDC group, only weight, BMI and insulin had changed. In the HDC group, BMI had decreased significantly in 25≤BMI subjects compared to 25>BMI subjects. In the 25≤BMI subjects, BMI decreased significantly more in the HDC group. Tea catechins are thus shown here for the first time to have the anti-obesity effects in humans.
Article
Coffee and tea are both drunk in most countries, but typically one predominates. Coffee is the preferred drink in Europe and the Americas, tea elsewhere. Until the early eighteenth century coffee production and consumption was confined to the Islamic world, tea production to East Asia. European traders altered this pattern dramatically. The present pattern of coffee consumption is influenced by income per capita, that of tea is not. Religious influences played some part in the early development of both tea and coffee but have little relevance at the present. National factors have influenced wider patterns. British preference for tea was taken to all their colonies. In recent years fears about health have had some influence on coffee consumption.
Article
An in vitro gastrointestinal model, which simulates the conditions in the human digestive tract, was used to determine potential antimutagenic activity of extracts of black tea and green tea. In this paper, results are presented on the availability for absorption of potential antimutagenic compounds present in tea and on the influence of the food matrix on this activity. Between 60 and 180 min after the tea was introduced into the model, antimutagenic activity was recovered from the jejunal compartment by means of dialysis: the dialysate appeared to inhibit the mutagenicity of the food mutagen MeIQx in the direct plate assay with Salmonella typhimurium (Ames test). The maximum inhibition was measured at 2 h after the start of the experiment and was comparable for black tea and green tea extract. To determine the influence of food matrices on the antimutagenic activity of tea, the model was loaded with black tea together with milk or a homogenized standard breakfast. The maximum inhibition observed with black tea was reduced by 22, 42 and 78% in the presence of whole milk, semi-skimmed milk, and skimmed milk, respectively. Whole milk and skimmed milk abolished the antimutagenic activity of green tea by more than 90%; for semi-skimmed milk the inhibition was more than 60%. When a homogenized breakfast was added into the model together with the black tea extract, the antimutagenic activity was completely eliminated. When tea and MeIQx were added together into the digestion model, MeIQx mutagenicity was efficiently inhibited, with green tea showing a slightly stronger antimutagenic activity than black tea. In this case, the addition of milk had only a small inhibiting effect on the antimutagenicity.
Article
During the last decade, the traditional notion that green tea consumption benefits health has received significant scientific attention and, particularly, the areas of cardiovascular disease and cancer were subject to numerous studies. Due to the ever-growing obesity pandemic, the anti-obesity effects of green tea are being increasingly investigated in cell, animal, and human studies. Green tea, green tea catechins, and epigallocatechin gallate (EGCG) have been demonstrated in cell culture and animal models of obesity to reduce adipocyte differentiation and proliferation, lipogenesis, fat mass, body weight, fat absorption, plasma levels of triglycerides, free fatty acids, cholesterol, glucose, insulin and leptin, as well as to increase beta-oxidation and thermogenesis. Adipose tissue, liver, intestine, and skeletal muscle are target organs of green tea, mediating its anti-obesity effects. Studies conducted with human subjects report reduced body weight and body fat, as well as increased fat oxidation and thermogenesis and thereby confirm findings in cell culture systems and animal models of obesity. There is still a need for well-designed and controlled clinical studies to validate the existing and encouraging human studies. Since EGCG is regarded as the most active component of green tea, its specific effects on obesity should also be investigated in human trials.
Article
Evaluation of the vitro antioxidant activity of green and black tea, their in vivo effect on plasma antioxidant potential in man and the effect of milk addition. The antioxidant activity of the tea, with and without milk, was tested in vitro by measuring the length of the peroxyl radical induced lag-phase. The in vivo activity was tested on two groups of five healthy adults. Each group ingested 300 ml of either black or green tea, after overnight fast. The experiment was repeated on a separate day, adding 100 ml whole milk to the tea (ratio 1:4 ). Five subjects acted as controls. The human plasma antioxidant capacity (TRAP) was measured before and 30, 50 and 80 min from the ingestion of tea. Both teas inhibited the in vitro peroxidation in a dose-dependent manner. Green tea was sixfold more potent than black tea. The addition of milk to either tea did not appreciably modify their in vitro antioxidant potential. In vivo, the ingestion of tea produced a significant increase of TRAP (P <0.05), similar in both teas, which peaked at 30-50 min. When tea was consumed with milk, their in vivo activity was totally inhibited. The paper shows that tea possesses a strong antioxidant activity in vitro which is believed to be exerted by its polyphenols moiety. It also provides compelling evidence that tea has also a potent in vivo activity in man. The promptness of the in vivo response suggests that the absorption of the bioactive components of tea takes place in the upper part of the gastrointestinal system. The inhibition of this effect by milk is thought to be due to the complexation of tea polyphenols by milk proteins. These findings might help to clarify the putative role of dietary poly- phenols in modulating oxidative stress in vivo.